Control Structures; Control Principle; Fc 360 Controls - Danfoss VLT FC 360 Design Manual

Product Overview

2.3 Control Structures

2.3.1 Control Principle

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A frequency converter rectifies AC voltage from mains into
DC voltage, after which this DC voltage is converted into a
AC current with a variable amplitude and frequency.
The motor is supplied with variable voltage/current and
frequency, which enables infinitely variable speed control
of three-phased, standard AC motors and permanent
magnet synchronous motors.

2.3.2 FC 360 Controls

The frequency converter is capable of controlling either
the speed or the torque on the motor shaft. Setting
1-00 Configuration Mode determines the type of control.
Speed control
There are two types of speed control:
•
Speed closed loop PID control requires a speed
feedback to an input. A properly optimised speed
closed loop control will have higher accuracy
than a speed open loop control.
Selects which input to use as speed PID feedback in
7-00 Speed PID Feedback Source.
Torque control
The torque control function is used in applications where
the torque on motor output shaft is controlling the
application as tension control. Torque control can be
selected in 1-00 Configuration Mode. Torque setting is done
by setting an analog, digital or bus controlled reference.
When running torque control it is recommended to make
a full AMA procedure as the correct motor data are of high
importance for optimal performance.
•
Open loop in VVC
in mechanical robust applications, but the
accuracy is limited. Open loop torque function
works for two directions. The torque is calculated
on basic of current measurement internal in the
frequency converter. See Application Example
Torque open Loop
Speed/torque reference
The reference to these controls can either be a single
reference or be the sum of various references including
relatively scaled references. The handling of references is
explained in detail later in this section.
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VLT AutomationDrive FC 360 Design Guide
plus
mode. The function is used
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MG06B202 - VLT is a registered Danfoss trademark